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Mechanical stress is an important regulator of bone metabolism. Fluid shear stress caused by mechanical load in bone tissue has been shown to be important to both the bone structure and function through its effects on osteocytes and osteoblasts. We thus explored the effects of continuous laminar fluid shear stress on the expression of growth factors and cytokines in human osteoblast-like SaOS-2 cells with a purpose-built cone-plate viscometer. We showed that the physiological level (1.7 Pascal) of continuous laminar fluid shear stress increased the mRNA expression of TGF-beta1 about three-fold after 3 hours and also increased TGF-beta1 protein about three-fold after 24 hours in the SaOS-2 cells. However, no mRNA expression of PDGF-A,IGF-II or IL-6 was detected. To explore the mechanism of up-regulation of TGF-beta1 expression, we examined the effects of a stretch activated cation nonselective (SA-cat) channel blockade with gadolinium and a voltage-dependent L-type Ca^<++> channel block
… Moreade with verapamil on the TGF-beta1 expression at the mRNA.levels. The shear stress-induced increase in the TGF-beta1 mRNA levels was thus significantly inhibited by both gadolinium and verapamil. These findings suggest that the physiological level of fluid shear stress induces the production of TGF-beta1 by the SaOS-2 cells via the cation influx and, as a result, may therefore promote bone formation.It is unclear how mechanical stress influences bone cells and regulates bone formation and resorption. We investigated the effects of continuous laminar fluid shear stress on human osteoblast-like osteosarcoma cells : SaOS-2 cells. The conditioned medium of the SaOS-2 cells after 24 hours of fluid shear stress significantly increased the formation of tartrate-resistant acid phosphatase (TRAP) positive cells to twice that observed in the control, using a human preosteoclastic cell-line : FLG 29.1 cells. IL-11 protein increased 7 fold in the conditioned medium of the SaOS-2 cells after 24 hours of fluid shear stress, using an enzyme linked immunosorbent assay (ELISA). IL-6, IL-1alpha and TNFalpha proteins were not detected in the conditioned medium. Northern blot analysis showed IL-11 mRNA increased 4 fold in the SaOS-2 cells after 6 hours of fluid shear stress. Furthermore, the addition of anti-human IL-11 antibody to the conditioned medium of the SaOS-2 cells after 24 hours of fluid shear stress significantly inhibited the increase in the number of TRAP positive FLG 29.1 cells. These findings suggest that fluid shear stress induces osteoblasts to stimulate osteoclast formation via IL-11 production. Less